This invention relates to an electron gun assembly having a pair of reinforced heater tabs each of which includes locating means to minimize cathode-ray tube, CRT, failure caused by a shorted conformal heater tab and to provide more accurate positioning of the conformal heater tab between the pair of reinforced heater tabs.
U.S. Pat. No. 3,555,640, issued to Lundvall on Jan. 19, 1971, discloses a method for mounting a heater within a tubular cathode. A U-shaped tab is welded to the legs of the heater, and a transverse portion of the tab is removed after the heater is positioned within the tubular cathode. The removal of the transition portion electrically isolates the arms of the tab so that the heater can be energized. The tab is shown as substantially flat; however, a step-like offset of the heater tab is shown in U.S. Pat. No. 4,523,124, issued to Blanken et al. on June 11, 1985. The offset facilitates centering of the heater within the tubular cathode and permits thermal expansion of the tab structure during tube operation, but provides little structural strength.
Copending U.S. patent application. Ser. No. 091,168 filed on Aug. 31, 1987, now U.S. Pat. No. 4,789,807 issued on Dec. 6, 1988 to the present inventor, discloses an inline electron gun assembly having at least one reinforced heater tab and, preferably, a pair of reinforced heater tabs which support and position the heaters for the outer cathodes of the inline electron gun. The reinforced heater tabs each include a main body portion, a pair of orthogonal legs extending from opposite sides of the main body portion and a pair of feet directed outwardly from the legs. Triangular gussets are formed between the main body portion and the legs and between the legs and the feet. The feet of each of the reinforced heater tabs are attached to the distal ends of oppositely disposed heater beads strap, the proximal ends of which are embedded into insulative support beads of the electron gun. The reinforced heater tabs are mutual parallel and provide a box-like structure with the support beads. A conformal heater tab. i.e., a heater tab without any reinforcing structure is disposed perpendicular to and attached between the reinforced heater tabs, preferably by welding. The feet of the conformal heater tab are attached to one of the legs of each of the reinforced heater tab in order to properly position the heater for the center cathode within the tubular center cathode. A drawback of this structure is that the feet of the conventional heater tab can be positioned anywhere along the legs of the reinforced heater tabs, and occasionally on one or both of the reinforcing gussets connecting the main body portion and the legs. Such misalignment of the conformal heater tab can result in the cathode heater contacting the tubular cathode sleeve, heat-sinking the heater, or, if the feet of the conformal heat tab are on the reinforcing gussets poor welding can occur which may result either in an open heater circuit or in weld-generated particles (i.e. weld-splash) within the electron gun.